Command migrate customers creates copies of user CT when output CT is not provided.

Prereq.: "Old" user CT exits, "new" customer CT exists.

Steps:

1. Execute command php bin/console ibexa:migrate:customers --input-user-group=INPUT-USER-GROUP --create-content-type and provide valid INPUT-USER-GROUP. Don't specify OUTPUT-USER-CONTENT-TYPE name.
2. Examine result.

Actual result: Error occurs "Argument '$contentTypeUpdateStruct' is invalid: Another Content Type with identifier 'customer' exists" but copies of user CT are created. Please see attached.
Expected result: Error occurs and new CT is not created until OUTPUT-USER-CONTENT-TYPE name is provided.